1. Field of the Invention
The present invention relates to a differential gear in an automobile, the gear having four differential pinions intermated with a pair of side gears and supported by pinion shafts arranged in a cross configuration.
2. Description of the Related Art
In the conventional differential gear of the type having four differential pinions, two typical arrangements are used for the differential case and the pinion shafts. One uses a cross-configuration unit pinion shaft, such as a spider 45, as exemplarily shown in FIGS. 5 and 6 of the attached drawings. In this arrangement, the differential case must be formed by two separate case members to allow the cross-configured unit pinion shaft 45 to be assembled in the case. The two separate case members are fixed to each other by bolts 46 after the elements, such as the pinion shaft 45 and differential pinion 44, are inserted. One problems that arises with this arrangement is that the separate case members must be specially machined to enable a precise assembly of the separate case members into a unit, resulting in a decrease in the productivity and assembling rate.
The other arrangement uses a split pinion shaft consisting of one long shaft and two short shafts, with the differential case having a unit wall structure. Japanese Unexamined Patent Publication No. 55-155946 discloses such an arrangement in which one long shaft and two short shafts are coupled together by an inner block. The outer ends of the shafts are received by apertures provided in the case wall and the apertures are partially covered by an outer ring member which restricts the radial outward movement of the shafts and allows the shafts to freely rotate. In FIG. 1 of that Publication, the outer ring is welded to the case. It is, however, impossible to disassemble the differential gear for service or repair if the outer ring is welded to the case. In FIG. 4 of that Publication, the outer ring consists of a discontinuous wire ring having elasticity. This may allow easy assembly and disassembly, but will not ensure that the outer ring is retained in place, or reliably retain the pinion shafts, since the outer ring is expandable. In general, the outer ring loosely holds the pinion shifts to enable the pinion shafts to freely rotate.
Japanese Unexamined Utility Model Publication No. 53-128632 discloses a differential gear having a single straight pinion shaft having notched ends. A discontinuous ring is mounted on the differential case to retain the pinion shaft. This ring is held in place by the outer ring gear. As in the previous case, however, the discontinuous ring cannot reliably retain the cross pinion shafts and the outer ring itself cannot be firmly retained since it is only surrounded by the outer ring gear.